Technical Field
The embodiments herein generally relate to a multiuser communication channel, and, more particularly, to a system and method of detecting multiuser based on symbol level interference cancellation at the soft demapper input in a receiver.
Description of the Related Art
In a wireless communication system, a central base station communicates with a plurality of remote terminals, such as cellular mobile phones. Frequency-Division Multiple Access (FDMA) and Time-Division Multiple Access (TDMA) are the traditional multiple access schemes to provide simultaneous services to a number of terminals. The basic idea behind FDMA and TDMA techniques is to slice the available resource into multiple frequency or time slots, respectively, so that multiple terminals can be accommodated without causing interference.
Contrasting these schemes with separate signals in frequency or time domains, Code-Division Multiple Access (CDMA) allows multiple users to share a common frequency and time channel by using code-division multiplexing.
Wideband Code Division Multiple Access (WCDMA) is an air interface standard found in 3G mobile telecommunications networks. WCDMA supports conventional cellular voice, text and MMS services, but can also carry data at high speeds, allowing mobile operators to deliver higher bandwidth applications including streaming and broadband Internet access. WCDMA has been developed into a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.
In WCDMA uplink receiver, each user is assigned a scrambling code which is a random sequence of length 38400. Although, these codes possess good autocorrelation and cross correlation properties, they are not perfectly orthogonal. This combined with multipath propagation makes WCDMA uplink receiver an interference limited system.
Due to the presence of interference, each user has to transmit at a higher power in order to meet the quality of service. This limits the coverage and capacity of the WCDMA uplink receiver. As a result, there is need for a technique for multiuser detection in the WCDMA uplink receiver. The typical multiuser detection involves jointly decoding all the user signals using the Maximum Likelihood (ML) criteria. But, the complexity of the typical multiuser detection increases exponentially with the number of users. A lot of emphasis has been on developing suboptimal methods for multiuser detection. In an existing interference cancellation method, each user's received signal is reconstructed and cancelled from the composite received signal. The interference cancelled signal is then processed to make the bit decisions better with iterations.
However, the major drawback of the conventional multiuser detection methods is due to high computational complexity involved. The extra complexity is not desirable at the low-cost base station, which possess limited memory and processing capacity.
Accordingly, there remains a need for a system and method that reduces storage requirement and processing capability during symbol level interference cancellation at a receiver, without compromising the receiver performance.